An optical modulation apparatus is an apparatus for adjusting a time in which a voltage is applied to a liquid crystal that is an optical modulation substance corresponding to prescribed data and for modifying the characteristics of transmitting lights by changing the torsion of a liquid crystal. The optical modulation apparatus is used mainly for an optical communication apparatus.
There are many kinds of liquid crystal panels that configure the optical modulation apparatus. One of them is called LCOS (Liquid Crystal on Silicon). The LCOS is provided with a structure in which a liquid crystal is disposed directly on a semiconductor substrate and bookended between transparent electrode and pixel electrode.
For the LCOS, a liquid crystal is disposed directly on a pixel electrode formed on the semiconductor substrate and is sealed. In the case of the LCOS, the pixel electrode formed on the semiconductor substrate is used as both of a reflecting plate and an electrode. Consequently, it is enough for a light to transmit one transparent electrode only, thereby improving a transmission factor.
Moreover, in the case of the LCOS, a wire can be disposed under the pixel electrode. Therefore, an aperture ratio of each pixel can also be improved by a width of the wire.
As described above, the LCOS has a high transmission factor and a high aperture ratio. Consequently, the LCOS has been started to be used for an optical modulation apparatus, a display and so on. In keeping with this trend, a lot of techniques related to the LCOS have been proposed (for instance, see Patent document 1).
A conventional art disclosed in Patent document 1 will be explained below. The conventional art disclosed in Patent document 1 is provided with a typical LCOS structure. A plurality of pixel electrodes are arranged on one plane, and a prescribed voltage is applied to each pixel electrode by a driver element. The pixel electrode and the driver element are connected to each other via a contact hole and a via hole.
Moreover, a light shielding layer for preventing a light from being applied to the driver element is disposed between the pixel electrode and the driver element to prevent a malfunction of the driver element.    Patent document 1: Japanese Patent Application Laid-open Publication No. 62 (1987)-169120 (Page 2, FIG. 1)
The conventional art disclosed in Patent document 1 shows a typical LCOS structure, and can also be used for a panel of an optical modulation apparatus. The present inventor has examined the case in which the conventional art disclosed in Patent document 1 is used for an optical modulation apparatus having a large pixel region, that is, a large light irradiation section.
In other words, the present inventor has examined the case in which the above described LCOS is used for an optical modulation apparatus that configures a TODC (Tunable Optical Dispersion Compensator).
Such a tunable optical dispersion compensator (TODC) will be explained below with reference to FIG. 7.
In FIG. 7, a numeral 100 indicates a tunable optical dispersion compensator (TODC) in the whole of the configuration.
In an optical communication field, optical data of a plurality of wavelengths are transmitted collectively through one optical fiber 102 to gain a bandwidth. However, a transmission of a long distance causes a phase of each wavelength to be misaligned.
Consequently, for the tunable optical dispersion compensator 100, lights that have transmitted through the optical fiber 102 are transmitted through a branching filter 104 to be separated for every wavelength by the branching filter 104. The lights separated for every wavelength by the branching filter 104 are then reflected to an LCOS 108 via an optical lens 106. A pixel electrode group of the LCOS 108 is then operated selectively to align a phase of each wavelength.
However, in the case in which the LCOS is used for the optical modulation apparatus, it is found that a shadow is generated in a pixel region to cause a reflection of a light to be nonuniform disadvantageously as described in the following.
In addition, in the case in which a high-intensity light is irradiated, a light leaks from a hole in a slit shape located around a pixel electrode connection to result in a malfunction of the driver element in some cases.
[Explanation of Problems: FIGS. 8 and 9]
With reference to figures, the following describes problems that occur in the case in which the conventional art disclosed in Patent document 1 examined by the present inventor is used for an optical modulation apparatus having a large pixel region. FIG. 8 is a schematic view for illustrating an LCOS having a large pixel region. FIG. 8(a) is a plan view, and FIG. 8(b) is a cross-sectional view taken along the line B-B′ of FIG. 8(a). FIG. 9 is a plan view schematically illustrating a display region shown in FIG. 8.
In FIGS. 8(a) and 8(b), a numeral 200 indicates an optical modulation apparatus in which an LCOS of a conventional art is used in the whole of the configuration.
In the optical modulation apparatus 200, a gate electrode 204 is formed on a substrate 202 made of a semiconductor substrate, and a drain region 206 and a source region 208 are formed around the gate electrode 204. The gate electrode 204, the drain region 206, and the source region 208 configure a driver element 210 of a MOS type transistor.
The driver elements 210 of MOS type transistors are electrically insulated and isolated by an element isolation region 212, and are electrically insulated and isolated by interlayer insulation films 214 and 216.
An optical protective film (a light shielding layer) 218 is formed on the upper surface of the interlayer insulation film 216, and a pixel electrode 222 is formed on the upper surface of the optical protective film (the light shielding layer) 218 via an interlayer insulation film 220.
The pixel electrode 222 and the driver element 210 disposed below the pixel electrode 222 are electrically connected to each other. That is to say, a wire 211 of the driver element 210 and the lower surface of the pixel electrode 222 are electrically connected to each other via a pixel electrode connection 224.
In this case, the pixel electrode connection 224 penetrates through a hole formed in the optical protective film (the light shielding layer) 218. A gap is formed between the pixel electrode connection 224 and an opening part formed in the optical protective film (the light shielding layer) 218. A slit 226 is formed around the pixel electrode connection 224.
Moreover, a final protective film 228 is formed on the upper surface of the pixel electrode 222, and a liquid crystal layer 229 is formed via the final protective film 228. A counter electrode (a transparent electrode) (not shown) is formed on the upper surface of the liquid crystal layer 229.
As shown in FIG. 8(a), the pixel electrode 222 is a rectangular electrode having a long side 222a and a short side 222b. The pixel electrodes 222 are arranged on two lines separately at regular intervals in such a manner that short sides 222b of adjacent pixel electrodes 222 face each other. Lights are irradiated to a region in which the pixel electrodes 222 are disposed. The area can be determined without any inhibition depending on the specifications of the optical modulation apparatus.
The area is composed of a plurality of pixel electrodes 222, and configures a light irradiation section 230 as shown in FIGS. 8(a) and 9.
For the pixel electrode 222, a size of the light irradiation section 230 is determined depending on the conditions of the optical system of an instrument in which the optical modulation apparatus is installed in a practical sense. In addition, the number of pixel electrodes 222 and the sizes of a long side 222a and a short side 222b are also determined. Consequently, a size of the pixel electrode 222 is extremely enlarged in some cases. For instance, a long side 222a is 1 mm and a short side 222b is 5 μm.
In the example shown in FIG. 8, the sizes of a long side 222a and a short side 222b are modified, and eight pixel electrodes 222 are arranged to improve visualization of the figure. FIG. 9 is a plan view for illustrating the entire of the light irradiation section 230.
As shown in FIG. 8, since the pixel electrodes 222 are arranged in an orderly fashion, the pixel electrode connections 224 for connecting the pixel electrode 222 and the driver element 210 to each other are also arranged in an orderly fashion, thereby configuring lines 232 of the pixel electrode connections 224.
Consequently, in the case in which the entire of the light irradiation section 230 is seen, a linear shadow 234 caused by the lines 232 of the pixel electrode connections 224 is generated as shown in FIG. 9.
In particular, an influence of the shadow cannot be ignored in a field that requires the reflection characteristics of high grade such as an optical communication field.
Moreover, a slit 226 is formed around the pixel electrode connection 224. The slit 226 is a slight opening portion of the optical protective film (the light shielding layer) 218 for a connection to the driver element 210.
The driver element 210 is located directly below the slit 226. Consequently, in the case in which a high-intensity light is irradiated, the light enters forcibly the slit 226, thereby resulting in a malfunction of the driver element 210 in some cases.
Therefore, in the case in which the conventional art disclosed in Patent document 1 is used for an optical modulation apparatus, in particular, an optical modulation apparatus having a large sized light irradiation section, a linear shadow is generated in the light irradiation section, thereby causing nonuniformity of a reflection. In the case in which a higher-intensity light is irradiated, a malfunction of the driver element occurs in some cases.
The present invention was made in order to solve the above problems of the conventional art. An object of the present invention is to provide an optical modulation apparatus that does not cause both of nonuniformity of a reflection and a malfunction of the driver element even in the case in which an area of the light irradiation section is large.